Hermetically sealed piezoelectric crystal holder



0a. 28, '1941. H. GRANGER 2,260,311

HERMETTCAHJY SEALED PIEZOELECTRTC CRYSTAL HOLDER Filed Dec. 27, 1940 2 Sheets-Sheet l IN VE N TOR Harold Granger BY ATTORNEY Oct. 28, 1941. H, GRANGER 2,260,311

HERMETICALLY SEALED PIEZOELECTRIC CRYSTAL HOLDER Filed Dec. 27, 1940 2 Sheets-$heet 2 INVENTOR Harold Granger ATTORNEY Patented Oct. 28, 1941 HERMETICALLY SEALED PIEZOELECTRIC CRYSTAL HOLDER Harold Granger, Alexandria, Va. Application December 27,1940, Serial No. 371,949

(01. Ill- 327) 16 Claims.

(Granted My invention relates broadly to piezoelectric crystal apparatus and more particularly to a holder for piezoelectric crystal elements by which long-time frequency stability may be obtained.

One of the objects of my invention is to provide a piezoelectric crystal holder in which the crystal is hermetically sealed in order to provide for long-time frequency stability by eliminating the effects of changes in barometric pressure and changes in relative humidity, in addition to the effects of dust and other foreign material.

Another object of this invention is to provide a hermetically sealed holder with provision for externally adjusting the size of the air gap between electrodes.

Another object of this invention is to provide a hermetically sealed externally adjustable holder which may be readily interchangeable with an existing type of holder.

The use of a piezoelectric crystal for frequency control or frequency measurement purposes generally requires that the final adjustment of the frequency be made while the crystal is operating in a suitable circuit. Since in the interest of long-time frequency stability it is desirable to eliminate the effects of changes in barometric pressure and changes in relative humidity, in addition to effects of dust and other foreign materials, it is desirable to provide a holder which can be hermetically sealed; in addition, it is desirable to be able to adjust the air gap between the crystal and one of the electrodes so that final adjustment of the frequency of the unit can be made while operating in its intended circuit. These requirements are met by this device.

My invention will be described in connection with the accompanying drawings, in which:

Fig. 1 is an elevation view of one design of a piezoelectric crystal holder of my invention;

Fig. 2 is a cross-sectional elevation view of the same design taken through the center line;

Fig. 3 is a cross-sectional plan View taken through the line 33 of Fig. 2;

Fig. 4. is a cross-sectional elevation View, taken through the center line of a modification of my invention; and

Fig. 5 is a cross-sectional plan view taken through the line 5-5 of Fig. 4. The two different designs are furnished to indicate the possible variations in construction of this device.

With reference to Fig. 2, a glass bead or seal ll acts as an insulator or dielectric for the electrical connection 22 to the upper electrode l8. The glass bead H is sealed to a glass sealing alloy tube 24 which is in turn sweated or welded to under the act of amended April 30, 1928; 370

dition to that March 3, 1883, as O. G. 757) a movable assembly consisting of plate 25, upper electrode l8, electrode insulating support l2, terminal insulator 20 and its support 2 I. This plate and assembly is attached to a metal bellows ill by welding or soldering and this bellows is in turn attached to the holder housing l9. Adjusting ring l4 bears upon the plate 25 and by rotation of the ring the bellows I5 is made to contract or allowed to expand, the expansion force being supplied by the natural spring of the bellows in adsupplied by a coil spring l6. An evacuation or filler port 25 is provided for the purpose of removing the air from the inside of the holder and introducing an inert gas or thoroughly dried air, after which the filler port may be sealed. Machine screws I3 used for supporting the upper electrode assembly are sealed by soldering over the heads.

This construction results in a hermetically sealed crystal holder, at the same time permitting external adjustment of air gap 23, thereby providing control of the frequency within limits determined by the characteristics of the crystal H, which is held by suitable means in contact with the holder housing l9 acting as a lower electrode.

Figs. 4 and 5 portray an additional design. This design is made primarily to provide a hermetically sealed adjustable air gap crystal holder in such form that it would be readily interchangeable with an existing type of holder.

With reference to Figs. 4 and 5, which are sectional drawings of the subject device, a glass bead or seal 30 is bonded to a glass sealing alloy tube 42 which is soldered or welded to a crystal holder casing 44. The glass bead 30 in this case is extended to provide a support for a terminal 3| to which is connected the electrical connection or conductor 32 for the upper electrode 31. The conductor 32 is in the form of a tube and permits the exit or introduction of gas or dry air from or to the interior of the holder, after which the tubular conductor is sealed. The conductor 32 is connected electrically to movable electrode 31 by flexible connector 40. A metal bellows 35 is attached by means of welding or soldering to a metal plate 45 to which is attached an assembly consisting of ceramic insulating support 46 and upper electrode 31. The opposite end of the bellows 35 is soldered or welded to the crystal holder casing 44. Soldering or Welding the bottom or fixed electrode 39 to the casing 44 completes the hermetic seal. Machine screws 34 supporting movable electrode assembly are sealed by soldering over Adjusting ring 33 bearing on plate the heads.

45 permits adjustment by contraction or expansion of the bellows 35. Expansion of the bellows is accomplished by the natural spring of same in addition to the force supplied by a coil spring 36. A stud 43 is rigidly secured to and projected from casing 44. The holder is supported by spring clips (not shown) which engage, respectively, terminal 3i and stud 43 and which are connected to an external circuit.

This construction provides a hermetically sealed holder and makes possible adjustment of the air gap 4| above piezoelectric crystal 38 providing a frequency control limited by the characteristics of the crystal.

The use of a hollow electrical connection from the external terminal of the upper electrode, as shown in Fig. 4, is not necessarily limited to Fig. 4, but might also have been used in the construction shown in Fig. 2. Also, the spring I 6 in Fig. 2 is shown located inside of the bellows and the corresponding spring 36 in Fig. 4 is shown located outside of the bellows. The location of the spring in either case has no bearing upon any electrical or mechanical properties of the device, but may be placed either inside or outside of the hermetically sealed chamber.

Other modifications and changes in the proportions and arrangements of the parts may be made by those skilled in the art without departing from the nature of the invention, within the scope of what is hereinafter claimed.

The invention described herein may be manufactured and/or used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What I claim is as follows:

1. A piezoelectric crystal holder, comprising in combination a casing acting as a lower electrode,

space with said crystal therein.

2. A piezoelectric crystal holder, comprising in combination a casing acting as a. lower electrode, an upper electrode insulated from said lower elecelectrode and said upper plate, ring bearing against said upper plate, said threads on said ring adapted to space between said electrodes, an upper plate attached to and insulated from said upper electrode, a spring between said lower electrode and said upper plate, an internally threaded adjusting ring bearing against said upper plate and adapted to cooperate with said external threads on said casing, said adjusting ring being adjustable to vary and adjust the size of said space between said electrodes, means to hermetically seal said space with said crystal therein, and means to connect said electrodes to an electric circuit.

5. A piezoelectric crystal holder, comprising in combination a casing acting as a lower electrode, an upper electrode insulated from said lower electrode, said holder adapted to accommodate a piezoelectric crystal in the space between said electrodes, means to connect said upper electrode to an electric circuit, means to connect said lower electrode to an electric circuit, means to vary and adjust the size of said space between said electrodes, an upper plate attached to and insulated from said upper electrode, a metal bellows between said lower electrode and said upper plate, a hermetic seal at the joint of said bellows and said upper sulated from said upper electrode, said upper plate having an opening, means to hermetically seal said opening after placing said first mentioned means therein, a metal bellows between mentioned means therein.

8. piezoelectric crystal holder, comprising in combination a casing acting means to vary and adjust the between said electrodes, a glass bead adapted to hermetically seal and surround said first mentioned means, a glass sealing alloy tube adapted to hermetically seal and surround said bead, an upper plate attached to and insulated from said upper electrode, having an opening adapted to receive said tube, a hermetic seal at the joint of said tube and said upper plate, a metal bellows between said lower electrode and said upper plate, a hermetic seal at the joint of said bellows and said upper plate, and a hermetic seal at the joint of said bellows and said lower electrode.

9. A piezoelectric crystal holder, comprising in combination a casing acting as a lower electrode, an upper electrode insulated from said lower electrode, said holder adapted to accommodate a piezoelectric crystal in the space between said electrodes, means to connect said upper electrode to an electric circuit, means to, connect said lower electrode to an electric circuit, means to vary and adjust the size of said space between said electrodes, an upper plate attached to and insulated from said upper electrode, a metal bellows between said lower electrode and said upper plate, a hermetic seal at the joint of said bellows and said upper plate, a hermetic seal at the joint of. said bellows and said lower electrode, an extended glass bead adapted to hermetically seal and surround said first mentioned means, a glass sealing alloy tube adapted to hermetically seal and surround said bead, said casing having an opening adapted to receive said tube, and a hermetic seal at the joint of said tube and said casing.

10. A piezoelectric crystal holder, comprising in combination a casing acting as a lower electrode, an upper electrode insulated from said lower electrode, said holder adapted to accommodate a piezoelectric crystal in the space between said electrodes, means to hermetically seal said space with said crystal therein, means to connect said upper electrode to an electric circuit comprising a tubular electric conductor adapted to pass through said first mentioned means, means to hermetically seal said tubular conductor, means to connect said lower electrode to an electric circuit, and means to vary and adjust the size of said space between said electrodes.

11. A piezoelectric crystal holder, comprising in combination a casing acting as a lower electrode, an upper electrode insulated from said lower electrode, said holder adapted to accommodate a piezoelectroc crystal in the space between said electrodes, means to hermetically seal said space with said crystal therein, means to connect said upper electrode to an electric circuit comprising a tubular electric conductor adapted to pass through said casing, means to hermetically seal said tubular conductor, means to connect said lower electrode to an electric circuit, and means to vary and adjust the size of said space between said electrodes.

12. A piezoelectric crystal holder, comprising in combination an externally threaded casing acting as a lower electrode, an upper electrode insulated from said lower electrode, said holder adapted to accommodate a piezoelectric crystal in the space between said electrodes, means to connect said upper electrode to an electric circuit, means to connect said lower electrode to an electric circuit, a glass bead adapted to hermetically seal and surround said first mentioned means, a glass sealing tube adapted to hermetically seal and surround said bead, an upper plate attached to and insulated from said upper electrode having an opening adapted to receive said tube, a hermetic seal at the joint of said tube and said upper plate, a metal bellow-s between said lower electrode and said upper plate, a hermetic seal at the joint of said bellows and said upper plate, a hermetic seal at the joint of said bellows and said lower electrode, a spring between said lower electrode and said upper plate, and an internally threaded adjusting ring bearing against said upper plate, said threads on said ring adapted to cooperate with said threads on said casing, said adjusting ring being adjustable to externally vary and adjust the size of said space with said crystal therein.

13. A piezoelectric crystal holder, comprising in combination an externally threaded casing, a lower electrode, a hermetic seal at the joint of said casing and said lower electrode, an upper electrode insulated from said lower electrode, said holder adapted to accommodate a piezoelectric crystal in the space between said electrodes, means to connect said upper electrode to an electric circuit comprising a tubular electric conductor adapted to pass through said casing, means to hermetically seal said tubular conductor, means to connect said lower electrode to an electric circuit, an upper plate attached to and insulated from said upper electrode, a metal bellows between said casing and said upper plate, a hermetic seal at the joint of said bellows and said upper plate, a hermetic seal at the joint of said bellows and said casing, an extended glass bead adapted to hermetically seal and surround said tubular electric conductor, a glass sealing alloy tube adapted to hermetically seal and surround said bead, said casing having an opening adapted to receive said tube, a hermetic seal at the joint of said tube and said casing, a spring between said upper plate and said casing, and an externally threaded adjusting ring bearing against said upper plate, said threads on said ring adapted to cooperate with said threads on said casing, said adjusting ring being adjustable to externally vary and adjust the size of said space with said crystal therein.

14. A piezoelectric crystal holder, comprising in combination a casing acting as a lower electrode, an upper electrode insulated from said lower electrode, said holder adapted to accommodate a piezoelectric crystal in the space between said electrodes, means including a spring to vary and adjust the size of said space, and means including a bellows to hermetically seal said space with said crystal therein.

15. A piezoelectric crystal holder, comprising in combination a casing acting as a lower electrode, an upper electrode insulated from said lower electrode, said holder adapted to accommodate a piezoelectric crystal in the space between said electrodes, means to vary and adjust the size of said space, and means including a bellows to hermetically seal said space with said crystal therein.

16. A piezoelectric crystal holder, comprising in combination a casing acting as a lower electrode, an upper electrode insulated from said lower electrode, said holder adapted to accommodate a piezoelectric crystal in the space between said electrodes, means including a spring to vary and adjust the size of said space, and means to hermetically seal said space with said crystal therein.

HAROLD GRANGER. 

